zc)()i,()(;kai, soc'irty bulletin 



1205 



stick are also useful for removing plauts and 

 other objects without putting the hands into 

 the water. 



One other aid in the management of the aqua- 

 rium sliould not be overlooked: A reliable book 

 on aquaria and their care is essential, and the 

 amateur will need to refer to it frequently. 

 There are books on this subject to be had at 

 most book stores. The New York Aquarium 

 has published a 63-page pamphlet on The Care 

 of Home Aquaria, which will be sent postpaid 

 for 27 cents. 



The small aquaria in the laboratory of the 

 New York Aquarium will be shown to visitors 

 making inquiry about them, and their manage- 

 ment in detail explained by those in charge. 



THE ASCTI)L\NS OR SEA-SQUIRTS. 

 Bif Raymond C. Osburn. 



THIS group of animals is distributed all 

 over the world in salt water, and several 

 species are common in this region, yet the 

 average person who finds them seems to have 

 not the slightest idea of what they are, or of 

 their relationships. Some of the.se are fre- 

 quently brought or sent to the Aquarium for 

 identification, and the questions which accom- 

 pany these requests for information are al- 

 most as interesting as the animals themselves. 

 "Please let me know what sort of sponge this 

 is and whether it has any value?" "I am 

 told that these things are 'Mother of eels.' What 

 are they and have they any connection with 

 eels.^"; "I am told that there is a good market 

 for these things for fish food. What is their 

 value and how are they prepared for market?"; 

 "These things are eating up the piles of my 

 boat dock. How can I get rid of them?"; 

 "What sort of fishes are these? There have 

 been thousands of them washed up on the 

 beach," etc., etc. 



However, when we consider that until less 

 than fifty years ago the zoologists were all 

 wrong with regard to the relationshi])s of this 

 group, we may jiardon the average person of 

 today for being misinformed concerning them. 

 The older naturalists placed some of them 

 among the sjionges. the zoophytes, the mollusca 

 and molluscoidea. The great Cuvier first gave 

 them a class name, Tunicata, and placed them 

 intermediate between the Radlata and Vermen 

 of his classification. It was not until in 18(31) 

 that Kowalevsky traced the development of the 

 larva and discovered that the ascidians are, in 

 fact, related to the vertebrates, but that, by 



■1 wonderful metamorphosis, the tiny tadpole- 

 like larva becomes transformed into a creature 

 so unlike a vertebrate that its real nature had 

 not been suspected. 



The ascidians {nscus^^a. sac), or tunicates, are 

 provided with an outer coat or tunic, secreted 

 bj' the ejiidermis, which consists of a substance 

 of the same chemical nature as cellulose, but 

 which, since it is found in animals instead of 

 plants, has received the name "tunicin." 



The tunicates fall naturally into three classes : 

 The Larvacea, Ascidiacea and the Thaliacea. 

 The first group includes a very few minute, free 

 swimming forms, which undergo no metamor- 

 phosis, and in which, therefore, the larval char- 

 acters are retained. These forms in the adult 

 stage retain the tail, which is pro\ided with a 

 notochord (the precursor of a vertebral column), 

 a complete dorsal, tubular nerve and gills which 

 open into the pharynx. While of great interest, 

 the}' are known onlj' to the zoologist, and need 

 not be further considered here. 



The Ascidiacea, or ascidians proper, are 

 numerous and widely distributed, occurring 

 from the Arctic regions to the equator and from 

 between the tide limits to great dejiths of the 

 ocean. Some of them have been dredged from 

 a depth more than three miles. Certain species 

 grow singh', others bud to form colonies, some 

 of these consisting of thousands of individuals. 

 In some cases the individuals are almost micro- 

 scopic in size, while in others thej' may reach 

 nearly a foot in length. They may be almost 

 transparent, or brilliantly colored, but frequent- 

 ly they are obscured by a layer of mud or sand 

 adhering to the tunic. On account of the rounded 

 form which many of these animals assume, they 

 were known to the ancients as sea-eggs and they 

 are still so called in many places by the fish- 

 ermen. 



Of the simple ascidians, Mogula manhatten- 

 sis (De Kay) is perhaps the commonest local 

 form. This species is often very abundant 

 about the docks and lives well in the Aquarium, 

 either in the balanced aquaria or in the larger 

 tanks supplied with the harbor water. This 

 is the species charged witli devouring the piles 

 of docks, though of course it is perfectly harm- 

 less and the real malefactor was merely ob- 

 scured beneath the layer of the Molgulas at- 

 tached on the surface. Also, this is the form 

 supposed to have a market value as fish food; 

 etc.. though, of course, it has none whatever. 



This common ^Slolgula is a small swollen sac, 

 resembling a small bladder, not more than an 

 inch in diameter, and is attached bv the tunic 

 at the side opposite the mouth. The mouth 



